In circulating fluidized bed boilers, many problems present themselves when attempting to recirculate the flow of high temperature (usually around 1,600.degree. F.) solids. Few systems exist that can accommodate such high temperature values especially when the material being transported is a dense combination of abrasive solids and high temperature gases. Additionally, the temperature of the transported material does not remain constant but instead varies as the use of or demand on the boiler varies. When demand is low, the to-be-recycled material can accumulate in the transport conduit creating a high temperature gradient across the system; and when demand is high, the temperature of the material flowing through the transport conduit is essentially the same as the temperature of the flue gas exiting the combustor.
Furthermore, high temperature values are not the only factors affecting the transfer conduit, instead, changes or swings in these temperature values (thermal shocking) also cause damage. Temperature swings on the order of several hundred degrees over a period of several minutes have been recorded. Also, large temperature differences oftentimes occur on opposite sides of the same pipe. Additionally, should pluggage occur in an upstream section of the system (such as in a hopper), tremendous transient forces can develop in the transfer conduit wherever the blockage is released. In one instance, the level of solids in a hopper was observed to drop five or six feet in about five seconds after one such blockage was removed.
Consequently, high temperatures and forces, and rapid swings in same, cause the transport conduit to undergo significant stresses and strains as well as thermal expansion and contraction. Attempts to support such a conduit, and allow for its thermal expansion and contraction, have to date not been satisfactorily applied to circulating fluidized bed boilers because of the abrasive material being transported, the temperature and pressure requirements and the size and weight of the transport conduit itself.
It is thus an object of this invention to provide a means for vertically supporting a high temperature conduit that is subject to temperature variations ranging from ambient temperature to 1,600.degree. F. or more as well as occasional rapid changes in internal forces. Another object of this invention is to provide a means for insulating this conduit and solidly supporting it within an outer casing. A further object of this invention is to provide a means of support that does not rigidly secure the inner conduit to the outer casing but instead allows the inner conduit to expand or contract as needed independent of the outer casing. These and other features will become obvious upon further investigation.